Data communication devices receive data from other data communication devices and/or transmit data to other data communication devices. Data communication devices are often addressable when more than two devices share a common communication channel. An address is a data code that uniquely identifies a device or a set of devices. When a data message transmitted through the common communication channel conveys an address, such as a phone number, path, ID code, or the like, a device that receives the data message decodes the address to determine what to do with the message.
Electronic tags represent one form of data communication device known to those skilled in the art. Electronic tags are low cost transponders which receive and transmit data messages via radio frequency (RF) signals. Typically, an interrogator transmits a data message which contains an ID code. All tags within range of the interrogator receive this data message. The ID code addresses a particular tag or category of tags. Each tag that receives the data message determines whether its ID or a category to which it belongs matches the address conveyed by the data message. If a tag determines that the data message is addressed to it, the tag processes the data message and typically responds by transmitting its own data message back to the interrogator.
Electronic tags are often battery powered. In order to increase battery life, conventional tags are maintained in a very low current, standby state until they sense RF energy from an interrogator. When a conventional tag detects such RF energy, it goes into a high current, operational state by powering up all its circuitry. Once operational, the conventional tag processes the received data message. In one of the first tasks performed after becoming operational, the conventional tag determines whether the received data message is actually addressed to the tag. If the data message is addressed to the tag, the tag continues to process the message and respond with requested information. After the tag completes the transaction, it again returns to its low current, standby state. If the data message is not addressed to the conventional tag, it directly returns to its low current, standby state.
This power management scheme works acceptably well in scenarios where tags are associated with moving objects, such as vehicles, railroad cars, trucks, or other objects which are interrogated only occasionally. However, where tags are associated with stationary objects, such as in a warehouse or inventory management environment, or with other objects which tend to receive numerous interrogations, battery life is severely shortened. In inventory management and other situations, many tags can be within range of an interrogator at all times. Each time an interrogator addresses an interrogation to a particular tag, all tags within range go to their high current, operational states. However, only the addressed tag actually processes the interrogation to any significant extent and responds to the interrogation.